Piezoelectric rotational motors are known having at least one piezo-electrically active part and one passive part, mounted with the capacity of relative movement in respect to each other and which interact with each other by friction.
A piezoelectric motor was chosen with a piezo-electrically active part comprising at least one oscillator of acoustic vibrations in the form of a planar ring-shaped piezoelectric element and flat pushers, mounted perpendicular with respect to the flat surfaces of the piezoelectric element and in acoustical contact with the flat pushers.
The disadvantage of this type of motor is that, with the perpendicular arrangement of the plane of the pushers in respect to the piezoelectric element surface, it is very difficult to create linear motors with high force or rotary motors with high starting torque. This is due to the low transmission efficiency of acoustic energy (vibrations) from the piezoelectric element to the pushers. Indeed, in a perpendicular arrangement of the pushers to the flat surface of the piezoelectric element, the acoustic energy supplied to each pusher comes through the pusher's edge, or a part of its surface, which greatly reduces the efficiency of such system.